public class String_Bulider {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        sb.append("你好");
        sb.append("你好2");
        sb.append("你好3");
        sb.append("165");
        sb.insert(3,"我的");
        System.out.println(sb);
        System.out.println(sb.indexOf("5"));
    }
}
